1. Field of the Invention
The present invention relates to a display apparatus for inputting video signals of various specifications, and more particularly, to a display apparatus having an improved structure in which all of current and future personal computer (PC) signals and high definition TV (HDTV) signals as well as normal TV signals can be displayed with optimum picture quality. The present application is based on Korean Patent Application No. 2001-74956, filed Nov. 29, 2001, which is incorporated herein by reference.
2. Description of the Related Art
Currently, the vertical frequency of a future HDTV mode is determined to be 50 Hz in China and Australia, and many problems are expected. That is, if video signals having a vertical frequency of 50 Hz are displayed on a display apparatus, flicker occurs. Also, if video signals having a vertical frequency of 50 Hz are converted into video signals having a vertical frequency of 100 Hz so as to reduce flicker, the horizontal frequency of the video signal is increased (around 55 Hz), and thus there is a problem in developing a deflection apparatus, a cathode ray tube, and a convergence controller, which correspond to the horizontal frequency of the video signal. As the horizontal frequency of the video signal is increased, the precision of control for deflection, the withstanding pressure of the cathode ray tube, and the precision of the convergence controller must all be increased.
The horizontal frequencies of a current cathode ray tube (CRT) are in the range of around 48 KHz, and the price of a CRT increases for CRTs beyond the range of 48 KHz, and thus profits for a display apparatus decrease.
In addition, in a multi-deflection mode, in which deflection parameters, which are appropriate for each of various frequencies are included and in which appropriate deflection parameters for an input video signal are selected and used, as the types (according to the input video signal specifications) of input video signals increase, it becomes increasingly difficult to maintain precise convergence, and thus the quality of the display apparatus is lowered.
FIG. 1 is a block diagram of the structure of a conventional display apparatus. The apparatus shown in FIG. 1 switches a normal PAL TV signal (625i/50 Hz) into PAL DTV signals in a R/G/B driver 108. Here, the vertical frequency of the input normal TV signal is 50 Hz but is converted into 100 Hz to reduce flicker. Here, i before “/” denotes interlaced scanning, and numerical values 50 and 100 after “/” denote vertical frequencies.
A problem common in display apparatuses is flicker. In particular, if normal TV signals of 50 Hz are displayed on a screen at a rate of 25 frames per second, frame flicker occurs.
The flicker detracts from viewing the screen and causes eye fatigue, and thus manufacturers of display apparatuses make an effort to remove or reduce flicker. The most general method for reducing flicker is to increase the vertical frequency of a video signal, that is, to increase the number of frames displayed per second.
Also, in the apparatus shown in FIG. 1, a normal TV signal having a vertical frequency of 50 Hz is converted into a signal having a vertical frequency of 100 Hz by a 100 Hz converter 106. In such a case, the horizontal frequency of the converted signal is around 31.5 KHz. Hereinafter, the phrase converted normal TV signal means a signal which has been obtained by converting a normal TV signal.
The input normal TV signal (RF or RGB) is input into a signal processor 102, and the signal processor 102 performs usual signal processing such as demodulation, elimination of noise, and compensation of picture quality. The normal TV signal output from the signal processor 102 is applied to the R/G/B driver 108 of the display apparatus so that a picture is reproduced.
The normal TV signal is converted into a signal having a vertical frequency of 100 Hz through an analog-to-digital converter (ADC) 104 and the 100 Hz converter 106 which is used to reduce flicker before being applied to the R/G/B driver 108.
The R/G/B driver 108 drives R/G/B electron guns (not shown) of a cathode ray tube (CRT) 110 by using a signal output from the 100 Hz converter 106.
The R/G/B driver 108 selects the converted normal TV signal or DTV signal, which is output from the 100 Hz converter 106, by switching.
The DTV signal may be formatted as 1080i/27 KHz, 576p/31.5 KHz, or 720p/38 KHz. Here, i and p before “/” denote interlaced scanning and progressive scanning, respectively, numerical values before “/” denote the number of effective vertical scanning lines (pixel numbers in the horizontal direction), and numerical values after “/” denote horizontal frequencies.
For example, 1080i/27 KHz means that the DTV signals have 1080 effective vertical scanning lines and are interlaced scanned, and have a horizontal frequency of 27 KHz.
The apparatus shown in FIG. 1 must deflect an input signal with different horizontal frequencies according to the type of input signal. That is, multi-deflection, which is equivalent to a horizontal frequency of 31.5 KHz for the converted normal TV signal and a horizontal frequency of 27 KHz, 31.5 KHz, or 38 KHz for DTV signal is required.
In the apparatus shown in FIG. 1, a mode discriminator 114 for recognizing the type of input signal, that is, whether the input signal is an analog signal or a digital signal, and the specifications of a digital signal, and a deflection driver 116 having a multi-deflection function for selectively providing a deflection operation that is appropriate for a signal displayed, with reference to the result of discrimination of the mode discriminator 114, are provided.
An operating voltage of a fly back transformer (FBT) used for deflection and a deflection yoke (DY) need to be changed into a desired voltage (e. g., 110 V˜100 V) according to the signal being displayed, and for this purpose, a mode controller 118 and a power supply (B+) controller 120 are provided.
A deflection signal output from the deflection driver 116 and B+ power supply provided by the power supply (B+) controller 120 is provided to a deflector 122.
Meanwhile, a controller 112 controls the signal processor 102, the analog-to-digital converter (ADC) 104, the 100 Hz converter 106, the R/G/B driver 108, the deflection driver 116, and the mode controller 118 depending on the result of the discrimination by the mode discriminator 114. A control operation by the controller 112 is done by using an I2C bus.
The apparatus shown in FIG. 1 uses a so-called multi-deflection method having various deflection modes corresponding to the various characteristics of different types of video signals, and thus has the following problems.
First, multi-deflection having various deflection parameters equivalent to various horizontal frequencies is required. As a result, high precision deflection, a high withstanding pressure, a method for high precision focus, and a method for driving convergence corresponding to multi-deflection are required, thereby increasing cost and lowering quality.
Second, there is a limitation in the type of signals which may be input. That is, the type of input signal that can be handled is limited by the limitations of the deflection apparatus, the CRT, and the convergence apparatus.
Third, it is difficult to accommodate a PC signal. Since it is impossible to implement a display apparatus so that the vertical frequency and horizontal frequency of a PC signal are compatible with those of a normal TV signal or DTV signal, it is difficult to fashion a display apparatus that can additionally display PC signals.